1. Field of the Description
The present description relates, in general, to design and control of robots including legged robots (e.g., floating-base, biped humanoid robots or other legged robots such as quadrupeds). More particularly, the present description relates to methods for developing, and then controlling, a robot to move in a manner that mimics or relatively closely matches an animation character's movements, e.g., a bipedal robot developed to walk like an animation or film character.
2. Relevant Background.
There is great demand for engineers and scientists in the robotic industry to create robots that embody animation characters in the real world, such as by taking on similar movements like a way of walking that is unique and readily recognized for the character. This is especially true in the entertainment industry because such character-imitating robots would allow people to physically interact with characters that they have previously only seen in films or on television shows. To give a feeling of life to these robots, it is important to mimic not only the appearance of the character being imitated but also to mimic the motion styles of the character.
Unfortunately, the process of matching the movements and motion styles of a robot to a character, such as a character in an animated film or television show, is not straightforward and prior solutions have not been wholly effective. One problem with designing and controlling a robot to mimic a character is that most animation characters are not designed and animated considering physical feasibility in the real world and their motions are seldom physically correct.
For example, it may be desirable to mimic a character that is humanoid in form, and a designer may choose to mimic the character with a biped humanoid robot, which is a robot with an appearance based on that of the human body. Humanoid robots have been designed for providing interaction with various environments such as tools and machines that were made for humans and often are adapted for safely and effectively interacting with human beings. In general, humanoid robots have a torso with a head, two arms, and two legs each with some form of foot such that the robot can walk on planar surfaces, climb steps, and so on (e.g., these humanoid robots are “bipeds” as are humans). Humanoid robots may be formed with many rigid links that are interconnected by joints that are operated or positioned by applying a force or torque to each joint to move and position a robot. Similarly, other legged robots such as those with three, four, or more legs also may walk utilizing force-controlled movement of their legs.
In order to interact with human environments, humanoid robots require safe and compliant control of the force-controlled joints. In this regard, a controller is provided for each robot that has to be programmed to determine desired motions and output forces (contact forces) and, in response, to output joint torques to effectively control movement and positioning of the humanoid robot. However, it has proven difficult to operate these humanoid robots with such a controller to accurately mimic an animation character's motion style as this style may simply not be physically correct or feasible for the humanoid robot and its links and joints (e.g., its physical components may not be able to perform the character's movements).
Animation characters have evolved to be more realistic in both their outer appearance and in their movements (or motion style). Using computer graphic techniques, three dimensional (3D) characters can be designed and generated with more natural and physically plausible motions with the 3D animation characters. Among many other motions, due to the interest in bipedal characters, generating realistic and natural bipedal walking has been extensively studied by many researchers. One approach to trying to mimic animation characters with bipedal robots has been to directly explore the walking motions with trajectory optimization to find desired motions that obey the laws of physics. Another approach has been to develop walking controllers that allow characters to walk in physics-based simulation. Recently, the computer graphics community has been trying to establish techniques to animate mechanical characters, and a computational framework of designing mechanical characters with desired motions has been proposed by some researchers. To date, though, none of these approaches has provided bipedal robots that consistently mimic an animation character's movements.
As a result, the desire to have lifelike bipedal walking in the real world has persisted in the field of robotics for the past several decades. To address the goal of solving real world problems such as helping elderly citizens in their daily life or resolving natural and man-made disasters, humanoid robots have been developed with high-fidelity control of joint positions and torques. Other bipedal robots that are more compact have been developed for entertainment and for hobby enthusiasts using servo motors. Recently, miniature bipedal robots with servo motors and links provided with 3D printers have begun to gain attention in the robotic industry. To date, though, none of these innovations have provided robots that can readily mimic movement, including walking, of many animation or film characters.
Hence, there remains a need for a method of developing/generating (and then controlling operations of) a robot that can more accurately move like a wide variety of animation characters, including characters that were not created to comply with constraints of the real or physical world. Preferably, the new method would at least be useful for developing a bipedal robot that walks like an animation character and, more preferably, would be useful for designing, building, and controlling a robot chosen to have a physical configuration at least somewhat matching that of the animation character so that the robot can be controlled to have the motion style of the animation character. Also, it may be useful in some implementations that the robots developed with these new methods be built using readily available components such as links that can be 3D printed and joints operated with servo motors and so on.